Field of the Invention
The present invention relates to a sheet conveying technique, and more particularly, to a purging technique.
Description of the Related Art
In general, a sheet conveying device mounted on an image forming apparatus such as a printer and a copying machine continuously conveys a plurality of sheets along one route. A printing process or the like is sequentially performed on these sheets at a high speed of several tens to several hundred or more of ppm.
When a jam (a paper jam) occurs at a certain position on the route, the image forming apparatus interrupts the process and causes a user to remove the jammed sheet. At this time, different sheets located before and after the jammed sheet are also forcedly stopped on the route. In order to resume the process, these sheets also need to be removed from the route in principle. However, the user feels troublesome whenever removing these sheets.
Among the sheet conveying devices of the related art, there is known a sheet conveying device devised for a user who feels troublesome in the sheet removing operation. Here, when the image forming apparatus interrupts the printing process or the like due to the jam or the like, all movable sheets are automatically discharged from the route. The sheet discharging operation which is performed by the sheet conveying device along with the process interrupting operation in the image forming apparatus will be referred to as a “purging operation”. Generally, the sheet as a purging target is discharged to a dedicated tray provided separately from a normal sheet discharging tray.
Patent Literature 1: JP 2014-119634 A
Since some space is needed for the installation of a purging tray, the image forming apparatus having the purging function is limited to a comparatively large-sized image forming apparatus so far. However, there is a demand for providing the purging function even in a medium-sized image forming apparatus used in an office or the like in accordance with the recent trend of the high functionality of the image forming apparatus.
Meanwhile, when the purging tray is provided in the medium-sized image forming apparatus, it is difficult to meet a decrease in size and cost strongly required in the medium-sized image forming apparatus.
As the medium-sized image forming apparatus used for an office, for example, an image forming system having a duplex printing function illustrated in FIG. 20 is known.
An image forming system 950 illustrated in FIG. 20 includes an image forming apparatus 900, a relay device 910, and a post-processing device 920. The image forming apparatus 900 is a color copying machine having a duplex printing function. In the duplex printing mode, the image forming system 950 performs the following operation.
First, Y, M, C, and K colors of toner images formed by an imaging part 901 are transferred in multiple layers onto an intermediate transfer belt 906 traveling in the circumferential direction as indicated by the arrow. The color toner images which are transferred onto the intermediate transfer belt 906 in multiple layers are secondarily transferred onto a front surface of a sheet SHT fed from a cassette 902 at a secondary transfer position 907.
When the sheet SHT having the toner images secondarily transferred thereonto passes through a fixing part 903, the toner image is fixed onto the front surface of the sheet SHT and the sheet SHT is guided to a reversing part 904 through a branch point 960.
The reversing part 904 reversely rotates the reversing roller 941 immediately before the tail end of the sheet SHT reaches the reversing roller 941 while the leading end of the sheet SHT is caused to protrude outward from the reversing port 940 provided in the casing by the reversing roller 941. Accordingly, the conveying direction of the sheet SHT is switched back (reversed). The reversed sheet SHT is guided to a circulation part 905.
The sheet SHT which is guided to the circulation part 905 is conveyed along a circulation path 951 and is returned to the secondary transfer position 907. During the circulating and conveying operation, a toner image forming operation is performed by the imaging part 901. Thus, when the sheet SHT passes through the secondary transfer position 907, the toner image on the intermediate transfer belt 906 is secondarily transferred onto the rear surface of the sheet SHT.
When the sheet SHT having the toner image secondarily transferred thereonto passes through the fixing part 903, the toner image is fixed onto the rear surface of the sheet SHT and the sheet SHT is conveyed from the branch point 960 to the post-processing device 920 through the relay device 910. In the post-processing device 920, post-processing such as a staple-binding process is performed on the sheet SHT and the post-processed sheet SHT is discharged.
By a sheet reversing mechanism having such a reversing port 940, a space necessary for switching back the sheet SHT is saved. Thus, if the outside of the reversing port 940 can be also used as a purging destination, a purging function can be provided in the image forming apparatus 900 while the casing of the image forming apparatus 900 is maintained in a small size.
As the purging function, for example, a function is considered in which sheets SH1 to SH3 are forcedly discharged to the outside of the apparatus from the reversing port 940 when the sheets SH1 to SH3 are conveyed inside the image forming apparatus 900 in the case where a jam occurs in a sheet SH0 of the post-processing device 920.
Incidentally, when the sheets SH1 to SH3 are continuously conveyed and the purging operation is performed while the sheets are guided to the reversing port 940 in an original conveying order, for example, an order of SH1, SH2, and SH3, there is a case in which a new jam occurs due to the collision of the sheet SH1 conveyed toward the reversing port 940 during the reversing operation of the sheet SH3 in accordance with the positions of the sheets SH1 to SH3 on the conveying route in the event of the jam (as indicated by the dashed line). In this case, the effort of the user in the sheet removing operation is not reduced.
Such a problem can generally occur in a sheet conveying device having the above-described reversing mechanism in addition to the sheet conveying device provided in the image forming apparatus.